Apparatus for applying atomized adhesive to a leadframe for chip bonding

ABSTRACT

An apparatus and method for evenly applying an atomized adhesive for bonding a die to a leadframe is disclosed. In one embodiment the apparatus includes a hood in communication with an air supply and a vacuum plenum that encompass a semiconductor device component located in a target area during adhesive application so that the adhesive is selectively applied to specific portions of the leadframe or other semiconductor device component and adhesive is not allowed outside the system. A mask or stencil may be employed for further prevention of adhesive application to undesired areas. An air purge may be employed to direct the adhesive mist toward the component to be coated. In another embodiment, a fine adhesive spray is directed against the surface of the workpiece to be coated, selected areas being masked to prevent coating. Wafers may be coated as well as leadframes.

CROSS REFERENCE TO RELATED APPLICATON

This application is a divisional of application Ser. No. 09/133,339,filed Aug. 13. 1998, pending, which is a continuation of applicationSer. No. 08/613,315, filed Mar. 11, 1996, now U.S. Pat. No. 5,810,926,issued Sep. 22, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a method and apparatus for bonding abare semiconductor chip or die to a leadframe and, more specifically, toa method and apparatus for injecting and applying an atomized adhesiveto a semiconductor device component.

2. State of the Art

A leadframe is basically the backbone of a typical molded plasticpackage. Leadframes serve first as a die support fixture during theassembly process and are subsequently electrically connected to the diebond pads after die-attach, as by wire bonding. After transfer molding,the leadframe becomes an integral part of the package. Generally,leadframes are fabricated from a strip of sheet metal by stamping orchemical milling (etching) and are made from various materials selectedfor cost, ease of fabrication, and various functional (mechanical andelectrical) requirements. Typical leadframe materials generally includenickel-iron, clad strip, or copper-based alloys.

An important feature of a leadframe is its ability to channel heat fromthe chip to the exterior of the package which is dependent on thethermal conductivity of the leadframe material. Copper alloy leadframesare desirable from this standpoint. However, copper alloy leadframesalso have high thermal-expansion rates (based on coefficients of thermalexpansion) in comparison to silicon, but nearly match the expansionrates of low-stress molding compounds. Consequently, the chip-bondingmaterial, that is, the die-attach material used to bond the chip to theleadframe, must be carefully selected. For example, silicon/goldeutectic bonding cannot be used with copper frames because its highelastic modulus couples thermally induced bending stresses generated byleadframe expansion to the silicon of the die, significantly increasingthe potential for die fracture As a result, silver-filled epoxies andpolyimide die-attach adhesives have been developed that are flexibleenough to accommodate the stress initiated by an expanding copperleadframe so that the die is not subjected to strain.

Leadframes are typically supplied in multi-frame strips designed withautomated assembly, wire-bond and packaging system in mind. As such,tooling or indexing holes are located along the leadframe-strip edges tomate with transfer-mechanism elements and alignment pins. Such pins aretypically part of the assembly equipment, including die bonders, wirebonders, molds, auto-inspection stations, trim and form equipment, andmarking machines.

As noted above, both silicon/gold eutectic as well as adhesive bondingmaterials have been used to bond the die to the leadframe. Forsilicon/gold eutectic bonding, the operation typically begins byindexing die on a bonding machine to a heated die support platform.Leadframes are then fed from magazines, along a track to a heater block.A small square of silicon/gold alloy (typically 6% Si, 94% Au) is cutfrom a feed ribbon and transferred to the die support platform, alsocalled a die-attach paddle, tab or island. Die and eutectic are thenscrubbed together, forming a hard alloy bond. The heater temperature isapproximately 420° C. and the total cycle time for eutectic bonding isabout 6 to 8 seconds.

Adhesive bonding is faster than eutectic, with a cycle time of about 2seconds. Typical feed mechanisms for polymer bonding machines are thesame as eutectic bonders. The leadframes, however, are usually notheated. Silver or gold-filled epoxy or polyimide adhesive paste istransferred to the die support platform by a print head, and a die ispressed into the paste immediately after printing. Die bonding adhesivesmanufactured by Epotek, Amicon and Ablestick are typically electricallyconductive, have maximum cure temperatures up to 275° C., and have lapshear strengths up to 2.11 kg/mm².

The die bonded leadframe strips are subsequently loaded into transportmagazines. Eutectic-bonded frames go directly to a wire bonding station,while magazines containing adhesive-bonded frames are routed to ovensfor curing. The curing atmosphere is typically dry nitrogen and usuallyrequires one hour at 150° C. to cure, followed by 30 minutes at 275° C.for polyimide adhesives.

A large number of polymers, copolymers, and polymer blends have beendeveloped in the past several decades with the aim of joiningcomposites. Epoxies, however, have been the primary material used tobond laminates, and such adhesives have been the principal bonding agentfor printed circuits. Due to their ability to react with many types ofcompounds and to enter solid solution with a variety of modifiers,epoxies can be formulated to meet most requirements that do not exceedtheir use temperature of 125° to 150° C. For thermoplastic adhesivesrequiring the adhesive material to be heated to temperatures around200-300° C., up to three hours of cure time may be required to removeany solvents. Epoxies, moreover, are generally very viscous andconsequently somewhat difficult to handle and apply.

Acrylics have been customarily used as adhesives for polyimides,requiring temperatures higher than the maximum use temperatures ofepoxies. Polyimidesiloxane hybrids have also been used that havesuperior thermal resistance and good compatibility for this purpose, Forapplications requiring the highest temperature or the most demandingdielectric requirements, polyperfluorocarbons may be used.Perfluorethylenepropylene copolymer films also exhibit suitable adhesionif the adherend surface is prepared properly.

Typically, rough or absorbent adherends readily bond together. Smooth,impervious materials, however, are much more difficult to adhere, andthese are more typical of printed-circuit substrates. Smooth surfaces,even if clean, usually cannot be bonded unless roughening or chemicaltreatment of the adherend surface precedes adhesive application. Metalsurfaces too smooth to be bonded can be roughened by abrasion, but morefrequently unalleviated metal surfaces as on power or ground planes areprepared for bonding by chemical modification. Alkaline oxidation ofcopper provides an instant oxide surface more polar and irregular thanthe original. Chelates such as benzotriazoles bond well to the oxidethat is always formed on copper and can be stable to 200° C. Thesechelates allow good adhesion to organics, have high cohesive strength,and serve as corrosion inhibitors when used as coatings.

Typical prior art devices apply (lie bonding adhesives by rolling,stamping, tape application, or spraying. That is, an adhesive-bearingroller or a stamp may be used to apply the adhesive to the die-attacharea of the leadframe. Similarly, a mask may be placed over the portionof the leadframe where adhesive is not desired and a spray nozzle mayspray the masked leadframes with the desired adhesive. Other methodshave also been developed, such as that disclosed in U.S. Pat. No.5,286,679, in which a patterned adhesive layer is deposited by hot orcold screen printing the adhesive, by photopatterning a photosensitiveadhesive, or by utilizing a resist method of etch back. Adhesive-coatedtapes have also been utilized to bond the die to the leadframe, asdisclosed in U.S. Pat. No. 5,304,842, as well as adhesive patchesapplied from tape carriers, as disclosed in U.S. Pat. No. 5,448,450.

The prior art systems, however, have several notable disadvantages. Forexample, such systems may not evenly distribute the adhesive across adie-attach paddle of the leadframe. Moreover, application of an adhesivehaving large particle sizes may cause voids or bubbles to form on theleadframe. Other adhesive applicator apparatuses do not draw theadhesive evenly onto the die-attach paddle or the leadfingers (in thecase of a leads-over-chip, or LOC, die-attach) and may have relativelyslow cycle times. In addition, many prior art systems do not fullyenclose or focus the adhesive application process to substantiallyreduce, if not substantially eliminate, contamination of equipmentcomponents and leadframe areas where adhesive is not desired. Prior artsystems may also require an additional, preliminary masking step in themanufacturing process to ensure that the adhesive is only applied todesired locations. Finally, many prior art systems may require anextended curing cycle in an oven, for example, to cure the adhesive orepoxy. In some systems, after die-attach, an optical alignment systemchecks to ensure that the die has been properly placed, translationallyand rotationally, on the leadframe. Between die-attach and wire bonding,however, dies requiring an extended epoxy cure cycle often have theirorientation or placement distorted as the adhesive cures, adverselyaffecting the wire-bond operation and, thus, quality and reliability ofthe product.

It is also desirable in some circumstances to apply adhesive to a wafersurface for so-called leads-over-chip or LOC mounting of a die under theleads of a leadframe without a die-attach paddle. Currently,screen-printing is employed to selectively coat the wafer.Alternatively, a spin-on process may be employed to coat the entirewafer surface, followed by selective etching away of the adhesive inundesired locations. Adhesively-coated tapes are also employed for LOCdie-attach. Such processes, as with those previously described, leavemuch to be desired in terms of process time, ease of use, and resultingproduct quality.

Thus, it would be advantageous to provide an apparatus for applying anatomized adhesive to a semiconductor device component for die bondingthat encloses the adhesive application process, evenly draws theadhesive onto the die paddle and removes excess adhesive, automaticallymasks or shields each component to protect certain areas from beingsprayed with adhesive, and has a relatively fast cycle time.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a method and apparatus forthe precise application of a die bonding adhesive to a semiconductordevice component using an injection nozzle to atomize the die-attachadhesive.

In one preferred embodiment, the apparatus includes a containment hoodwith an associated spray nozzle in communication with an adhesivereservoir and positioned above an adhesive application location ortarget area. An air purge may be incorporated within the hood to drivethe adhesive onto the die-attach paddle area for a further reduction incycle time. In addition, the plenum of a vacuum or negative-pressuresystem may also be positioned on the opposite side of (usually below)the adhesive application location from the injection nozzle to help drawthe adhesive onto the die paddle and carry away any excess atomizedadhesive. The hood and/or lower vacuum system may be connected to a camsystem or other mechanism as known in the art that allows forsimultaneous opening and closing of the hood and/or vacuum plenum aroundthe target area to allow indexing of semiconductor device componentsthrough the apparatus. Further, the apparatus preferably utilizesflexible seals on the edges of the hood and lower vacuum assembly tocontain the adhesive application process to the area where adhesivedeposition is desired, When the apparatus is used to apply adhesive toleadframes the seals may contact the dambars and side rails of theleadframe to provide the maximum amount of vacuum and adhesive leakagefrom the target area.

In one aspect of a preferred embodiment the apparatus has a shutter-typemechanism that opens an aperture above the leadframe, allowing a vacuumto draw the atomized adhesive mixture evenly onto the die-attach paddlefor a specified cycle time. Preferably, the adhesive is atomized to aparticle size of 50-100 μm. The aperture is sized and shaped to covervarious portions of the leadframe to shield those portions and preventapplication of adhesive thereto.

After a leadframe has been fed into the target area, the die paddle willbe located under the hood. The leadframe may be optically and/ormechanically aligned by methods known in the art. A mechanical alignmentsystem employing the leadframe strip indexing holes is preferred forsimplicity and substantial immunity to contamination by adhesive. Thecam system then closes and seals the hood and the vacuum assembly plenumabout the leadframe. A shutter positioned above the leadframe opens anda mask covers the surrounding area of the leadframe that does notrequire any adhesive. The injection nozzle inside the hood injects,under high pressure, a selected quantity of adhesive that atomizes andmixes with air provided to the containment hood from an exterior source,which is normally outside of the clean room where the adhesiveapplication apparatus is located. The vacuum below the leadframe pullsthe atomized adhesive particles downwardly and deposits them evenly ontothe die paddle.

Using an electronic or mechanical timing device, the shutter may bereleased to close once a pre-defined amount of adhesive has beeninjected. The shutter, as well as dictating exposure of the leadframe tothe adhesive mist, also substantially prevents adhesive dripping. Forfaster cycle times, an additional air purge within or above the hood andbehind or above the atomizer nozzle can be utilized to apply a small airburst or puff to help accelerate and direct the adhesive toward theleadframe. After the adhesive has been applied, the shutter closes, thecam system opens the hood, and a feed mechanism indexes the leadframetoward the next position. By design, the apparatus of the invention canbe placed in an otherwise conventional die-attach sequence in place offor example, a conventional epoxy stamp.

The hood, shutter mechanism, and vacuum system preferably incorporateone or more drainage channels for collection and removal of excessadhesive. If the volume of air under the hood becomes oversaturated withadhesive, for example, causing the adhesive to drip, the drainagechannels can collect the adhesive and recycle it to the adhesivereservoir. Cleaning the system of the invention should be less frequentthan other spray-type systems because the excess adhesive is pulled intoa recirculating or disposal system.

In another preferred embodiment, the hood, vacuum system, and shuttercan be modified to simultaneously accommodate multiple leadframes, ifdesired, such that the adhesive could be applied across all desiredleadframe areas of a leadframe strip simultaneously in one cycle.

Preferably, the adhesive employed with the application system of theinvention should have characteristics similar to epoxies currentlyavailable. That is, the adhesive must be conductive and may be coloredor otherwise detectible by an automatic imaging system. Further, theadhesive should be provided in liquid form or liquefied prior toatomization by heating to a desired viscosity for proper atomization.Adhesives having a relatively low solvent content would have the effectof greatly reducing the amount of cure time. Moreover, use of such anadhesive formulated to have a cure time of 10 seconds or less afterapplication to the die paddle could eliminate the entire oven-cureprocess and provide for immediate, aligned attachment and immobilizationof the die on the leadframe. Moreover, an adhesive having thesecharacteristics could reduce total process time by 2-3 hours byeliminating elevated temperature cure time in an oven. In selecting suchan adhesive, the effects of temperature encountered during a transfermolding or other encapsulation process should also be considered.

The apparatus and method herein described will prevent excess adhesivefrom being deposited on the leadframe, provide more precise and evenlydistributed adhesive application, increase the reliability of theprocess, and produce faster cycle times than prior art systems.Moreover, an increased adhesion area of adhesive will result due to thesmall particle size of the atomized adhesive, eliminating uncoatedinter-particle spaces and filling any voids or vugs on the surface ofthe leadframe or other semiconductor device component. The potential forbubbles or voids within the adhesive layer will also be substantiallyreduced as compared to application of thicker, more viscous epoxies usedin the art.

In another preferred embodiment, an adhesive spray may be aimed toward awafer instead of being misted and then drawn toward the target by airflow. For example, a wafer is loaded onto a working platen by amechanical loading arm. Once on the platen, the wafer is held in placeby a vacuum and aligned by an imaging alignment system using fiducialmarks as known in the art After alignment, a stencil is automaticallyplaced on the surface of the wafer to mask the areas where adhesive isnot desired. The hood then seals around the wafer periphery and a spraynozzle aimed toward the wafer deposits an even coating of adhesive. Thespray nozzle may be translatable along a spray path over the wafer, ormultiple nozzles used on a fixed or translatable spray bar. Multiplepasses of the nozzle(s) could thus be made depending on the spray area,adhesive volume delivered per pass, and adhesive thickness desired. Thestencil is then removed and the wafer unloaded by a mechanical arm. Theprocess is then repeated for other wafers. When sufficient adhesivematerial accumulates on the stencil, the stencil is removed and replacedwith a clean one. Alternatively, the stencil may be cleaned after eachwafer, or the stencil fabricated from a disposable material anddiscarded after one or more uses.

Similarly, when spraying leadframes according to the above-describedembodiment, a mechanical arm or conveyor loads a leadframe or strip offrames to an adhesive application location or target area. When theleadframe or strip is properly positioned and masked by stencil, ifdesired, a sensor stops leadframe movement and the spray nozzle ornozzles deposit the adhesive. When spraying is complete, the stencil islifted, and the leadframe or strip is removed by the mechanical arm ormoved along by the conveyor to the pick-and-place die-attach station.The invention thus reduces cycle time through full automation of theequipment, reduction in the number of cleaning cycles, and reducedadhesive application and die-attach time The system has utility with alltypes of leadframes, including those with a die-attach paddle as well asLOC lead frames, for which it is particularly well-suited.

In either system described above, the machine parameters such as spraypressure, temperature, nozzle height, nozzle speed, nozzle type, nozzleaperture size, spray pattern, cycle time, and (where applicable) vacuumor negative pressure below the target area would be dependent on theadhesive material used and desired thickness of the adhesive. It shouldbe noted that references to adhesives and other bonding agents in thespecification and claims comprise adhesives such as epoxies as well asall other sprayable bonding materials as known in the art.

In addition, the invention disclosed herein has equal application andutility with regard to the coating of leadframes, leadframe strips,conductor-carrying boards and other substrates, semiconductor wafers,partial wafers and singulated dies, although the latter may not bepractical for high-volume operations. Thus, the use of the term"semiconductor device component" as used in the specification and claimsconnotes any of these items, and contemplates the application ofadhesives thereto.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view of an adhesive application apparatus inaccordance with the present invention;

FIG. 2 is a perspective view of the adhesive application apparatus ofthe present invention showing its alignment with a typical LOCleadframe,

FIG. 3 is a schematic drawing of a typical leadframe with a die paddleshowing the position of the adhesive application apparatus in dashedlines;

FIG. 4 is a schematic drawing of the adhesive application apparatus inconjunction with a cam system to open and close the apparatus;

FIG. 5 is a schematic drawing of an adhesive application apparatus ofthe invention for adhesive application to wafers;

FIG. 6 is a schematic drawing of a stencil positioned over a wafer;

FIG. 7 is a schematic drawing of another preferred embodiment of anapparatus in accordance with the present invention; and

FIG. 8 is a top schematic elevation of a stencil covering a strip ofleadframes.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, an exemplary leadframe 12 is shown positioned within thetarget area of an adhesive application apparatus 10 of the presentinvention. Leadframe 12 includes a die-attach paddle 14 and leadfingers16 (see FIG. 3), in this instance, the paddle 14 being downset from thefingers 16, as known in the art. The apparatus 10 is comprised of acontainment hood 18 and a vacuum system 20. The hood 18 as shown has atapered configuration, being wider near the leadframe 12 and narrowingtoward its distal end, where it is connected to feed air duct 22, whichprovides air from a source exterior to the containment hood. The hood 18could have any configuration as long as the adhesive application processcan be suitably focused and contained. The hood 18 has an adhesive port24, through which a delivery tube 26 extends. The tube 26 communicateswith an adhesive reservoir 28 at its first end 30 and a nozzle 32 at itssecond end 34. The nozzle 32 is preferably an atomizer nozzle capable ofdispersing adhesive 36 supplied by the adhesive reservoir 28 at aparticle size of 50-100 μm. Adhesive may be supplied under pressure byuse of a pressurized gas as a propellant, a positive-displacement pump,or by other means known in the art.

Duct 22 above applicator hood 18 is connected to a positive- orambient-pressure clean (filtered and of controlled humidity) air supplyas known in the art so that air 40 can enter the hood 18 and carry theatomized adhesive 38 downward. The air 40 and atomized adhesive 38 mixin a mixing chamber 42 formed by the hood 18. An aperture panel or mask44 covers portions of the leadframe 12, such as the leadfingers 16 inFIG. 1, where adhesive 38 is not desired.

Below the leadframe 12, the vacuum system 20 provides a negativepressure zone such that adhesive 38 is quickly drawn downward ontoleadframe 12, with the excess pulled into the vacuum system 20 so thatonly the upper side of the leadframe is coated with adhesive byreduction of backspatter, and to reduce lateral overspray potential. Thevacuum system 20 is shown to have a plenum 21 similar in shape to thehood 18, but may have any configuration suitable to draw the adhesive 38through the leadframe 12. The negative pressure can be as great or aslittle as desired dependent upon various process parameters such ascycle time, adhesive particle size, and desired thickness of adhesivelayer. Moreover, as the vacuum system 20 collects the excess orover-sprayed adhesive 38, the unapplied adhesive can be recycled to theadhesive reservoir 28 by recycling system 39 as known in the art throughtube 41

In addition to the air 40 provided by feed duct 22, a gas purge 46 fedfrom a compressed or pressurized gas source of adequate quality may beincorporated into or above the hood 18 as shown to provide puffs orbursts of air to accelerate and directionalize the adhesive 38 towardthe leadframe 12 and minimize lateral dispersion of the mist. The gaspurge 46 may be necessary to further reduce cycle times.

The containment hood 18 may also include a shutter 48 positioned at ornear the bottom of the chamber 42 and above the leadframe 12. Shutter 48may be laterally translatable and may comprise a two-panel arrangementextendable and retractable from opposing sides of hood 18 for more rapidclosure. The shutter 48 is positionable over the leadframe 12 to preventadditional adhesive 38 from being deposited onto the die paddle 14 aftera predetermined period of time. Thus, the nozzle 32 atomizes theadhesive 38. and the adhesive 38 is drawn onto the die paddle by the air40 and, if desired, driven by the air purge 46. After a desired volumeor layer thickness of the adhesive 38 is deposited on the die paddle,the shutter 48 closes until another leadframe 12 is positioned withinthe apparatus 10. The hood 18, aperture panel 44, and shutter 48 mayalso collect and recycle excess adhesive 38 using drainage channelsattached to, or formed in, their surfaces. Aperture panel 44 and shutter48 may be combined.

As shown, the lower edge 50 of the hood 18 and the upper edge 52 of thevacuum system plenum 21 are provided, respectively, with resilient orflexible seals 54 and 56. Seals 54 and 56 may comprise, for example,flexible skirts or compressible elastomers. The seals 54 and 56respectively engage with the upper and lower surfaces of leadframe 12when the apparatus 10 is in a closed position, such that the adhesiveapplication process is substantially contained within a defined area. Assuch, components and equipment external to the hood 18 and vacuum system20 are not exposed to adhesive 38, and atomized adhesive 38 is notexposed to stray air currents in the assembly area.

The leadframe 12 or a strip of frames may be carried into the targetarea under the containment hood 18 on a carrier to protect (mask) thelower surface against backspatter during adhesive coating. A strippablepolymer film might also be employed to cover that surface. The leadframemight also be superimposed over or even placed on a backspatter barrierThe upper surface of the barrier is cleaned, or the barrier replaced,when contaminated by adhesive. Element 15 of FIG. 1, shown in brokenlines, depicts placement of such carrier, film or barrier with respectto leadframe 12.

Referring to FIG. 2, the relative size and shape of the hood 18 andvacuum system plenum 21 in relation to an exemplary LOC leadframe 62 ofone embodiment of the present invention is shown. As shown in dashedlines, the adhesive application location or footprint 58 extends aroundthe leadfingers 60 such that only those portions of the leadframe 62where adhesive 38 is desired are exposed to the adhesive applicationprocess of the present invention. The footprint 58 may also extend tothe dambars 55 or siderails 57 to enhance sealing with hood 18 andvacuum system plenum 21. If so, an aperture panel or mask 44 would bedesirable to shield selected portions of the leadframe 62, As shown, thehood 18 has an opening 63 to allow lateral insertion and retraction ofthe shutter 48, it being understood that a sliding seal would beprovided between the periphery of opening 63 and shutter 48. Similarly,FIG. 3 shows an exemplary footprint 64 of a hood 18 in relation to anexemplary leadframe 12 with a die-attach paddle 14. As shown, thefootprint 64 may extend to the side rails 65 and dambars 67 to achievethe best seal. Flow area 66 between peripheral hood footprint 64 anddie-attach paddle 14 should be carefully considered with the pressurebalance of the system to provide for adequate fluid flow past leadframe12.

FIG. 4 shows a cam 70 and linkage structure 72 attached to the hood 18and vacuum system 20 to open and close the adhesive applicationapparatus 10. The linkage structure 72 is comprised of an L-shapedmember 74 linking the hood 18 to the cam 70 and an L-shaped member 76linking the vacuum system 20 to the cam 70. Between the cam 70 and thehood 18, the L-shaped member 74 is translatably attached to elongatesupport members 78 and 80 by pins 82 and 84, respectively. Likewise,between the cam 70 and the hood 18, the L-shaped member 76 istranslatably attached to elongate support members 78 and 80 by pins orbushings 86 and 88, respectively. At their proximal ends 92 and 94, theL-shaped members 74 and 76 are attached to rollers 96 and 98,respectively In addition, the L-shaped members 74 and 76 are biased bysprings 90. The spring 90 biases the L-shaped members 74 and 76 towardeach other. Cam 70 may be driven between two positions as shown by apneumatic hydraulic or electric (linear motor) cylinder 93 through a rodand pivot linkage 95 as shown. The cam 70 may also be driven by a rotaryelectric motor or a pneumatic or hydraulic drive system that is capableof varying speeds and/or incremental rotation. In either sucharrangement, as the cam 70 rotates, depending on the position of the cam70 relative to the rollers 96 and 98, the hood 18 and the vacuum systemplenum 21 are either in a closed or open position.

Other methods and structures known in the art can be used to engage anddisengage the hood 18 and the vacuum 20 in a cyclic manner. In addition,those skilled in the art will appreciate that it may not be necessary tomove both the hood 18 and/or the vacuum system 20, depending on thesystem employed to position leadframes 12 at an adhesive applicationlocation. For example, a conveyor system may be able to simply moveleadframes through the apparatus without having to raise and lower upperand lower components if, for example, movable seals are employed at theinlet and outlet sides of the target area.

FIG. 5 shows another preferred embodiment in which a translatable nozzle100 directs an adhesive spray 102 within target area 103 onto thedesired device component 104, in this case an uncut wafer 104 held on aworking platen 105 having a vacuum retention system. The nozzle 100 maybe translatable within a spray containment surround 106 in both an X andY direction, that is, across the entire surface 108 of the wafer 104,and may comprise multiple nozzles on a spray bar (shown in broken lines)translatable in one or more directions. One or more optical ormechanical alignment sensors 125 as known in the art may also be used toproperly align the wafer 104 and/or the stencil 110 with respect to thewafer 104 (if not preassembled before placement in the target area), ifrequired. As shown, the wafer 104 is covered by a stencil 110 thatallows adhesive 112 to deposit on desired locations 114 of the wafer 104while being blocked by the stencil 110. A vacuum system 116 below targetarea 103 may optionally provide a negative pressure such that any excessspray of the adhesive 102 is removed from the target area. This negativepressure, however, is not required and if used, is not of great enoughmagnitude to cause turbulent flow across the stencil 110 After adhesiveapplication, the wafer 104 can be indexed through the opening 124 andanother inserted through opening 126 by, for example a mechanical arm128 or other conveyor mechanism.

The stencil 110 as employed in FIG. 5 is shown from above in FIG. 6superimposed on wafer 104 and has a semicircular outer surface 118 witha flat 120 across one end to match the wafer flat. The stencil 110 hasopenings 122 sized, shaped and positioned to match the individual dielocations of the wafer 104. The stencil 110 is positioned over the wafer104 with a mechanical arm or other means known in the art. An optical ormechanical alignment system 125, as known in the art, may be employed toensure exact alignment of stencil 110 with wafer 104.

The same type of directed or aimed spray nozzle or nozzles 100 can beused to apply adhesive 102 to a leadframe 130, shown schematically inFIG. 7 as an LOC leadframe. As shown, a leadframe 130 (which may alsocomprise a strip comprised of multiple frames) is conveyed by a conveyorsystem 132 comprised of a first conveyor guide rail 134 and a secondconveyor guide rail 136. Guide rails 134 and 136 are preferably U-shapedwith their open ends receiving the side edges of the leadframe ormultiple-frame strips. Both the first and second conveyor rails 134 and136 have associated transfer-mechanism elements and alignment pins 138that may engage the tooling or indexing holes 140 in the leadframe 130responsive to the output of a sensor 135 detecting the presence orposition of the leadframe. As such, the conveyor system 132 can properlyposition the leadframe relative to a nozzle 100, which is configuredsuch that the periphery of spray pattern 142, as shown in broken lines,only extends to the inner ends of leadfingers 144. Of course, a mask mayalso be used to delineate the spray pattern. Any spray that fallsbetween the leadfingers 144 can be collected by a vacuum system 116,reducing the necessity for, and frequency of, cleaning.

If one desires to simultaneously apply adhesive to multiple frames of aleadframe strip (see FIG. 2), a multi-aperture mask or stencil 150 asshown in FIG. 8 may be useful. As shown, the stencil can be positionedover a leadframe strip such that only the leadfingers 152 (or die-attachpaddles, if a conventional leadframe) are exposed through the openingsor apertures 154 of the stencil 150. Thus, adhesive 102 can be appliedto multiple leadframes simultaneously, requiring fewer cycles of theadhesive application apparatus 10.

It should be understood that various epoxies and other adhesives may besuitable for use in this apparatus. Preferable adhesives which may beformulated for use with the invention include polyimides and siloxanepolyimides (also termed polyimide siloxanes), the latter providingenhanced adhesion and increased flexibility in comparison to the former.Moreover, the orientation of the apparatus as shown in the preferredembodiments is for illustration only and, while preferred to takeadvantage of gravitational forces, may therefore be altered as desiredwithout departing from the scope of the accompanying claims.

Having thus described in detail preferred embodiments of the presentinvention, it is to be understood that the invention defined by theappended claims is not to be limited by particular details set forth inthe above description as many apparent variations thereof are possiblewithout departing from the spirit or scope thereof.

What is claimed is:
 1. An apparatus apparatus for applying a liquifiedadhesive to a semiconductor device component for die bonding,comprising;a containment hood; a spray nozzle configured and positionedto direct the liquified adhesive in said containment hood; a target areapositioned in communication with said containment hood and located in anintended path of the liquified adhesive so that said intended path willimpinge a semiconductor device component in said target area; aconveyor; and a negative pressure plenum adjacent said target area,substantially opposite from said spray nozzle.
 2. The apparatus of claim1, wherein said adhesive spray nozzle comprises an atomizing spraynozzle.
 3. The apparatus of claim 1, further comprising a movableshutter positionable across said spray path.
 4. The apparatus of claim1, further comprising an actuator for moving said containment hoodrelative to said target area.
 5. The apparatus of claim 1, furthercomprising an actuator for moving said negative pressure plenum relativeto said target area.
 6. The apparatus of claim 1, further comprising agas purge associated with said adhesive spray nozzle and positionabletoward said target area.
 7. The apparatus of claim 6, wherein said gaspurge is disposed above said adhesive spray nozzle.
 8. The apparatus ofclaim 1, further comprising sealing members associated with saidcontainment hood and said negative pressure plenum.
 9. The apparatus ofclaim 8, wherein said sealing members are adapted to contact thesemiconductor device component during application of the liquifiedadhesive thereto.
 10. The apparatus of claim 9, wherein thesemiconductor device component comprises a leadframe having a die-attachpaddle, and said sealing members are arranged to surround a periphery ofsaid paddle.
 11. The apparatus of claim 9, wherein the semiconductordevice component comprises a leadframe including dambars, and saidsealing members are alignable with at least some of said dambars toenhance sealing contact with said leadframe.
 12. The apparatus of claim1, further comprising an adhesive reservoir in communication with saidadhesive spray nozzle.
 13. The apparatus of claim 1, further comprisinga mask within said target area.
 14. The apparatus of claim 1, furtherincluding an adhesive recycling system.
 15. The apparatus of claim 1,further comprising an air source associated with said containment hood.16. An apparatus for applying a liquified adhesive material to asemiconductor device component for die bonding, comprising:a containmenthood; a spray nozzle configured and positioned to direct the liquifiedadhesive material in an intended spray path through a portion of saidcontainment hood; a conveyor; a target area positioned in communicationwith said containment hood and located within said intended spray pathof the liquified adhesive material so that said intended path willimpinge a semiconductor device component in said target area; and anegative pressure plenum in communication with said containment hood,said negative pressure plenum positioned on a substantially oppositeside of said target area from said adhesive spray nozzle.
 17. Theapparatus of claim 16, further comprising a movable shutter positionablein said spray path between said adhesive spray nozzle and said targetarea.
 18. An apparatus for applying a liquified adhesive material to asemiconductor device component, comprising:a containment hood; a spraynozzle configured and positioned to direct a stream of liquifiedadhesive in said containment hood; a negative pressure plenum incommunication with said containment hood, said negative pressure plenumbeing positioned substantially opposite said spray nozzle; a conveyor;and a target area positioned in communication with said containment hoodand with said negative pressure plenum, said target area being locatedin an intended path of said liquified adhesive from said spray nozzle sothat said intended path will impinge a semiconductor device component insaid target area, substantially between said spray nozzle and saidnegative pressure plenum.
 19. The apparatus of claim 18, furthercomprising an actuator for moving said containment hood relative to saidtarget area.